Internal combustion engines may utilize direct fuel injection, wherein fuel is directly injected in to an engine cylinder to improve combustion mixture preparation and to reduce cylinder charge temperatures. An amount of time a direct fuel injector is activated may be a function of fuel pressure supplied to the injector, engine speed and engine load. Therefore, at higher pressures, a fuel pulse width supplied to the injector may be adjusted to a short duration of time (e.g., less than 500 micro-seconds). However, operating the fuel injector with short pulse widths may cause the injector to operate in a non-linear or ballistic region where the amount of fuel injected may vary substantially for small changes in the fuel pulse width. For example, the direct fuel injector may deliver less fuel than desired in the ballistic region where shorter pulse widths are applied to the fuel injector. Further, the variability in the ballistic region may not show a linear trend. Also, fuel injectors delivering fuel to the cylinder often have piece-to-piece and time-to-time variability, due to imperfect manufacturing processes and/or injector aging (e.g., clogging), for example. Consequently, injector variability may cause cylinder torque output imbalance due to the different amount of fuel injected into each cylinder, and may also cause higher tail pipe emission and reduced fuel economy due to an inability to correctly meter the fuel to be injected into each cylinder. For at least these reasons, it may be desirable to re-characterize fuel injector flow, in particular in the ballistic operating region, during a life cycle of the engine.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for a cylinder, comprising: splitting injection of a fuel amount into a plurality of injections during a cylinder cycle in response to a request to characterize a control parameter of a fuel injector delivering fuel to the cylinder; adjusting the control parameter based on an exhaust lambda value; and operating the fuel injector based on the adjusted control parameter.
By splitting a fuel injection amount into a plurality of split fuel injections during a cylinder cycle, it may be possible to provide the technical result of learning a fuel injector transfer function or gain without having to operate the cylinder with an engine air-fuel ratio that may be leaner or richer than is desired. In particular, a pulse width supplied to the fuel injector to deliver each of the plurality of split fuel injections may be adjusted to be short enough in duration to operate the fuel injector in its non-linear low flow region. A correction factor for adjusting the fuel injector transfer function or gain may be determined based on an engine lambda value determined at an exhaust gas oxygen sensor. For example, as the number of fuel injections increase, the pulse width of each split fuel injection during the cylinder cycle decreases. Consequently, if fuel supplied by the fuel injector in response to the pulse width is less than a desired amount, the transfer function correction factor may be determined based on a change in lambda value from a nominal lambda value observed during a nominal single fuel injection. In this way, by splitting the fuel injection into multiple split fuel injections and measuring the engine lambda signal, it may be possible to characterize the fuel injector in the non-linear region while operating the engine at the desired air-fuel ratio.
The present description may provide several advantages. In particular, the approach may reduce engine air-fuel errors. Additionally, the approach may allow a fuel injector to be operated at pulse widths that were heretofore avoided because of non-linear fuel injector behavior, thereby extending the range of injector operation. Further, the approach may reduce engine emissions and improve catalyst efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.